Improve outline fonts and colors (#63325)

Closes https://github.com/zed-industries/zed/issues/58580

* Outline modal and panel now use buffer fonts for the contents:

<img width="1728" height="1117" alt="modal"
src="https://github.com/user-attachments/assets/5e0ef6e3-be39-4949-bc32-7087a51a02ec"
/>
<img width="1728" height="1092" alt="panel"
src="https://github.com/user-attachments/assets/5cf9edbf-5ff3-402d-a2ca-bc915bd10e8e"
/>

* Gutter colors are now fall-backed to tree-sitter better, if no
semantic tokens could be retrieved due to multi buffer shenanigans:

<img width="1728" height="426" alt="gutter"
src="https://github.com/user-attachments/assets/a175b2c8-843e-4632-b030-3edfbd350982"
/>

Release Notes:

- Improved outline fonts and colors

crates/syntax_theme/src/syntax_theme.rs

@@ -2,6 +2,7 @@
 
 use std::{
     collections::{BTreeMap, btree_map::Entry},
+    ops::Range,
     sync::Arc,
 };
 
@@ -61,6 +62,14 @@ impl SyntaxTheme {
         self.highlights.get(highlight_index.into())
     }
 
+    pub fn resolve_runs<'a, Id: Into<usize> + Copy + 'a>(
+        &'a self,
+        runs: impl IntoIterator<Item = &'a (Range<usize>, Id)> + 'a,
+    ) -> impl Iterator<Item = (Range<usize>, HighlightStyle)> + 'a {
+        runs.into_iter()
+            .filter_map(|(range, highlight_id)| Some((range.clone(), *self.get(*highlight_id)?)))
+    }
+
     pub fn style_for_name(&self, name: &str) -> Option<HighlightStyle> {
         self.capture_name_map
             .get(name)